1. Field of the Invention
This invention relates to a method for reducing the amount of arsenic emitted as a sublimate from the combustion of a fuel containing arsenic. It also relates to improved fuel compositions that will, when combusted, leave an ash that retains substantial proportions of the arsenic originally present in said fuel composition.
2. Prior Related Art
Many fuels such as crude shale oil, coal tar distillates, and certain coals contain appreciable proportions of arsenic. When continuously burned from a stationary source, such as a power plant, these fuels emit arsenic as a sublimate which, upon condensation, can act as a carcinogen and, possibly, a poison. Also, by condensing in a form which is usually water soluble, soil run-off may increase the arsenic concentration of the local water supply to intolerable levels.
Additionaly, even the presence of arsenic in the air is a source of concern. In the United States, proposed OSHA regulations would limit the arsenic concentration in the air to which workmen could be exposed for 8 hours to no more than 0.002 mg/m.sup.3. This limit may be difficult to meet, especially for power plants and the like that burn arsenic containing fuels. For example, it is reported in Chemical Abstracts, Vol. 72, 1970, Abstract No. 24286 K that two Russian power plants burning arsenic containing coals emitted sufficient arsenic to increase the arsenic concentration in the air to a maximum of 0.003 and 0.010 mg/m.sup.3 at a distance of 1 km from the respective plant sites. Despite the obvious problems relating to the discharge of such high concentrations of arsenic, the only proposed solution reported in the Abstract was to increase the height of the power plant stacks, thereby dispersing the arsenic over a wider area.
Other attempts to prevent arsenic emissions under such circumstances have focused on removing the arsenic from the fuel itself. As an example, it is known that arsenic can be removed from shale oils by passing them over a nickel-molybdenum catalyst under hydrotreating conditions. However, in addition to their high maintenance and capital costs, such processes are useless for removing arsenic from coals.
Therefore, it is one objective of the invention to provide a method for burning an arsenic containing fuel, including coals, so as substantially to reduce the arsenic sublimate emissions produced therefrom. It is another objective to provide arsenic containing fuel compositions that will, upon combustion, leave an ash retaining substantial proportions of said arsenic. It is another objective to retain the arsenic in said ash in a form that is essentially water insoluble or unleachable, thereby rendering it innocuous to soils and water supplies. Other objectives and advantages will appear from the specification herein.